1. Field of the Invention
The invention in general relates to fluid flow measurements, and particularly to a flowmeter which utilizes lasers.
2. Description of the Prior Art
In ultrasonic flowmeters for measuring velocity or volumetric flow rate of a fluid in a pipe, acoustic energy is propagated from an upstream transducer to a downstream transducer, and vice versa, and the difference in transit times of the oppositely directed acoustic energy is utilized in the computation of fluid flow. Various other systems for example use the difference in phase oppositely directed acoustic signals while still other systems utilize a sing around technique either along a single path or along two closely spaced parallel paths, to obtain a frequency difference indicative of fluid flow.
Many such systems utilize transducers which are inserted through the walls of the fluid carrying pipe but not to an extent where the transducer would intrude into the flow. Since one or more transducers are pointed downstream and one or more transducers are pointed upstream at an angle to the pipe axis, there is a small notch or protrusion formed in the inner surface of the pipe. For some measuring systems, this discontinuity could have an adverse affect on the fluid flow which could degrade system accuracy. Further, depending upon the fluid being measured, a discontinuity may represent a location for solid particulate to collect, which, after a period of time, might block or degrade the acoustic signal.
In other types of flowmeter systems transmitter and receiver transducers are coupled to the outside of the pipe and the acoustic signals are propagated through the pipe wall, undergoing refraction at the fluid-inner wall surface interface. When measuring fluid velocity acoustically, it is desirable to have the acoustic path at a small an angle as possible with respect to the pipe axis. For example with transducers which penetrate the pipe wall a practical minimum angle is in the order of 30.degree.. With the clamp on transducers however the practical minimum angle may range from approximately 65.degree. to 75.degree..
In the present invention acoustic waves are generated at a minimum angle of 0.degree. with respect to the pipe axis and without the requirement of any protrusion into the fluid.
In many of these acoustic systems an acoustic pulse with a fast rise time is a primary requirement in order to obtain high accuracy in the transit time measurement. The improved flowmeter described herein produces an acoustic pulse with an extremely fast rise time surpassing that produced by a conventional transducer, with the added feature that the pulse is generated directly in the fluid under measurement.